1. Field of the Invention
This invention relates to an apparatus for controlling timings of motion of inlet and outlet valves of cylinders in a multiple-cylinder internal combustion engine, the apparatus having a function of discriminating the cylinders with respect to their operation cycles.
2. Description of the Prior Art
Some of internal combustion engines include a crankshaft, a camshaft for cylinder inlet valves, and a camshaft for cylinder outlet valves. The crankshaft is connected to the camshafts by a power transmission mechanism so that the crankshaft will drive the camshafts. Generally, the camshafts rotate at half the speed of rotation of the crankshaft.
Cylinder discriminating apparatuses for multiple-cylinder internal combustion engines detect, for example, which of cylinders will fall into a specified condition in its operation cycle next or which of cylinders will undergo an ignition process next. Generally, the detected information is used in spark timing control or fuel injection control. The cylinder discriminating apparatuses include angular sensors associated with an engine camshaft for detecting the angular position thereof.
Variable valve timing mechanisms for internal combustion engines adjustably vary the angular relation of at least one of engine camshafts with an engine crankshaft.
In the case where both the cylinder discriminating apparatus and the variable valve timing mechanism are provided on an internal combustion engine, the information generated by the angular sensor in the cylinder discriminating apparatus tends to be inaccurate since the variable valve timing mechanism changes the angular relation of an engine camshaft with an engine crankshaft.
Japanese published unexamined patent application 5-10227 discloses a cylinder discriminating apparatus for an internal combustion engine which includes a cylinder discrimination sensor installed on a camshaft. The apparatus of Japanese application 5-10227 is designed to prevent erroneous Judgment of a cylinder in the case where the engine is provided with a variable valve timing mechanism which relatively varies a phase relation between the camshaft and a crankshaft. In the apparatus of Japanese application 5-10227, reading of an output signal of the cylinder discrimination sensor is stopped at the time of switching a valve timing, and the cylinder discrimination is performed based on a cylinder discrimination condition which occurs before the time of switching the valve timing.